Hardening agents for image-receiving elements

ABSTRACT

THE PROCESS OF HARDENING A POLYMERIC PHOTOGRAPHIC IMAGE-RECEIVING LAYER CONTAINING RADICALS SELECTED FROM THE GROUP CONSISTING OF -OH, -NH2 AND -SH RADICALS, INCLUDING THE STEPS OF ADDING TO A SOLUTION OF THE POLYMER A CROSS LINKING AGENT WHICH IS A CONDENSATE OF ACROLEIN AND EITHER A TETRALOWERALKOXY-PROPANE OR A LOWER ALKYLMONOALDEHYDE OTHER THAN FORMALDEHYDE, AND THEREAFTER CASTING AND DRYING A LAYER OF THE SOLUTION.

United States Patent 3,586,503 I-IARDENING AGENTS FOR IMAGE- RECEIVING ELEMENTS Lloyd D. Taylor, Everett, Mass, assignor to Polaroid Corporation, Cambridge, Mass. No Drawing. Continuation-impart of abandoned application Ser. No. 229,194, Oct. 8, 1962. This application Dec. 30, 1966, Ser. No. 605,971

Int. Cl. G03c 5/54 U.S. CI. 96-29 7 Claims ABSTRACT OF THE DISCLOSURE This application is in part a continuation of my 00- pending U.S. application Ser. No. 229,194, filed Oct. 8, 1962, now abandoned.

This invention relates to photography and more particularly to novel products and processes.

One object of this invention is to provide an improved image-receiving element for color diffusion transfer processes, in which a polymeric image-receiving layer has been hardened by the hereinafter specified class of hardening agents.

Another object of this invention is to provide a process for hardening polymer-containing image-receiving layers for use in color diffusion transfer processes.

Still another object of this invention is to provide novel color diffusion transfer processes utilizing said image-receiving layers.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the process involving the several steps and the relation and order of one or more of such steps with respect to each of the others, and the product possessing the features, properties and the relation of elements which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description.

The present invention is particularly related to color diffusion transfer processes. In such processes, a sheet of photosensitive material is exposed to create therein a latent image. The latent image is developed and, concurrent with and under the control of this development, an imagewise distribution of diffusible color-providing materials is formed. At least a portion of these diffusible color-providing materials is transferred by means of an alkaline aqueous processing liquid to a superposed imagereceiving layer to form a color image thereon. As examples of such processes, mention may be made of the processes claimed and disclosed in U.S. Pat. No. 2,983,606, issued May 9, 1961, wherein dye developers (i.e., dyes containing a silver halide developing function and capable of developing exposed silver halide) are the color-providing materials; the processes claimed and disclosed in U.S. Pat. No. 2,647,049, issued July 28, 1953, to Edwin H. Land, wherein color developers are employed to develop the latent image and color couplers are the colorproviding materials; the processes disclosed in U.S. Pat.

3,586,503 Patented June 22, 1971 ice No. 2,774,668, issued Dec. 18, 1956, to Howard G. Rogers, wherein complete, preformed dyes which are capable of coupling are used as the color-providing substances; and the processes disclosed and claimed in U.S. Pat. No. 2,968,554, issued Jan. 17, 1961, to Edwin H. Land.

The image-receiving elements used in such processes generally comprise an opaque or transparent support coated with an image-receiving layer of a dyeable material which is permeable to the alkaline aqueous processing solution. In the past, it has been proposed to use filmforming materials, such as polyvinyl alcohol, and nylons, such as N-methoxy-methyl-polyhexamethylene adipamide, as the dyeable materials. A preferred image-receiving element utilizes poly-4-vinylpyridine and, more preferably, a mixture of poly-4-vinylpyridine and polyvinyl alcohol, such as is disclosed in U.S. Pat. No. 3,148,061, issued Sept. 8, 1964, to Howard C. Haas.

The above described image-receiving elements have been found to be particularly useful in color diffusion transfer processes which employ dye developers. The improvements have been especially marked when azo and anthraquinone dye developers are employed. Dye developers, as noted above, are compounds which contain in the same molecule both the chromophoric system of a dye and also a silver halide developing function. They may be further defined as dyes which are silver halide developing agents. By a silver halide developing function is meant a radical capable of developing an exposed silver halide image. Particularly useful dye developers are those in which the silver halide developing function is provided by the presence of a benzenoid developing radical. A preferred benzenoid developing radical in such compounds is a hydroquinonyl radical. Examples of representative dye developers are given in the previously mentioned U.S. Pat. No. 2,983,606, and in applications to which crossreference is made therein.

In color diffusion transfer processes employing dye developers, an exposed silver halide emulsion is developed in the presence of the dye developer and, as a result of this development, the dye developer in the developed areas is oxidized and substantially immobilized. At least a portion of the immobilization is believed to be due, at least in part, to a change in the solubility characteristics of the dye developer upon oxidation and especially as regards its solubility in alkaline solutions. In unexposed and partially exposed areas of the emulsion, the dye developer is unreacted and diffusible, and thus provides an imagewise distribution of unoxidized dye developer, dissolved in the liquid processing composition, as a function of the point to-point degree of exposure of the silver halide emulsion. At least part of this imagewise distribution of unoxidized dye developer is transferred, by imbibition, to a superposed image-receiving layer or element, said transfer substantially excluding oxidized dye developer. The imagereceiving element receives a depthwise diffusion, from the developed emulsion, of unoxidized dye developer without appreciably disturbing the imagewise distribution thereof to provide a reversed or positive color image of the developed image.

The presence of water-sensitive film-forming materials in the image-receiving element often results in swelling of the film during processing with a resulting distortion of the image. Such water sensitivity can be minimized or eliminated by hardening or cross-linking the polymer, prior to photographic processing, with aldehydes such as glyoxal as is disclosed in U.S. Pat. No. 3,033,872, issued Oct. 10, 1961 to Elkan R. Blout et al. However, while hardening the polymer, such materials may also introduce photographically adverse side effects, such as loss of gloss, reduced image density, and adhesion of the processing composition to the receiving layer. In order to prevent such adhesion of the processing composition, an additional coating or layer may be applied, but this so-called strip coat, as well as introducing an additional step into the fabrication of the image-receiving sheet, may also interfere with the transfer of dye developers to the re ceiving sheet, as do some of the hardening or cross-linking agents, resulting in an over-all diminution of positive image quality.

A class of compounds has now been found that unexpectedly meet most if not all the problems above enumerated, in that (a) the polymer in the receiving element is readily hardened with the desired degree of water insensitivity and without loss of gloss, and (b) the receiving element can be stripped cleanly from its superposed position with no adhesion thereto of the processing composition, without the necessity of an additional strip coat on the receiving sheet, and without an adverse effect on the stability of the transfer dye image.

The above enumerated results may be achieved by treating receiving sheets containing polymers with OH, NH or SH groups with certain hereinafter designated acrolein condensates.

The acrolein condensates suitable as hardening agents within the scope of this invention comprise a condensate of acrolein and a lower alkylmonoaldehyde or a tetraloweralkoxypropane. In general, the condensates are low molecular weight materials, preferably having an average molecular weight within the range of about 120 to 600 and the lower alkyl and lower alkoxy radicals of the monoaldehyde and propane, respectively, comprise three or less carbon atoms.

As examples of compounds within the generic designation suitable for reaction with acrolein to form the stated acrolein condensates, mention may be made of monoaldehydes such as formaldehyde, acetaldehyde, propionaldehyde,

(Glyceraldehyde) and 1,1,3,3-substituted propanes such as CHsO OCH;

(1, 1, 3, S-tetramethoxypropane) CH3 CHzO CH3 H-CCH2-CH (1, 1, 3-trimethoxy-3-ethoxypropnne), and

CHaCHgO OCHzCHt' HC- CHz-OH CH3 CHzO O CHzCHa (1, 1,3, 3-tetraethoxypropane) Acrolein condensation reactions are well known to those skilled in the art; see, for example, US. Pats. Nos. 3,080,281, issued Mar. 5, 1963, and 3,183,054, issued May 11, 1965, to Rudolph F. Fisher et al. Such a reaction may be carried out by mixing, in an acidic medium, in varying mole ratios, acrolein and the aldehyde or propane identified above. The product may then be diluted, e.g., to a 50% aqueous solution by weight for ease of handling, or used directly in hardening the receiving layers without dilution.

The following nonlimiting example illustrates the preparation of an acrolein condensate suitable for use as a hardening agent within the scope of this invention.

EXAMPLE 1 11.2 gm. of acrolein, 15.2 gm. of 1,l,3,3-tetramethoxypropane and 1 drop of phosphoric acid were mixed in a beaker. 26.4 gm. of water was then added to provide a 50% aqueous solution by weight.

As an example of a commercially available acrolein condensate suitable for use in this invention, mention may be made of Aldocryl Resin X-12, a trade name for a low molecular weight condensate of acrolein and formaldehyde sold by Shell Chemical Company, New York, N.Y. Aldocryl Resin X-l2 is described as a storage stable, pale yellow, 50% by weight aqueous solution with a mildly irritating odor and has the following average properties: an average molecular weight of 180-200; a viscosity at 20 C. of 6.65 centipoises; a density at 20 C. of 1.135 gm./ml.; a pH of 4 to 5; a carbonyl value of approximately 1.20 equivalents per gm. of solution and a complete solubility in water and ether.

The term acrolein, as used herein, is intended to include not only CH CHCHO, propenal (acrolein), but also acrolein dimer, both in its monomeric and polymeric form, as well.

As examples of polymers suitable for use with the hardening agents of this invention, mention may be made of polyvinyl alcohol, gelatin, partial acetals of polyvinyl alcohol, such as those disclosed in US. Pat. No. 3,239,337, issued Mar. 8, 1966 to Howard C. Haas, cellulose, cellulosic derivatives and other carbohydrate polymers.

The novel hardening agents of this invention are water soluble and can therefore be easily incorporated into the receiving element by adding an aqueous solution of the hardening agent to the polymer solution just prior to casting the polymeric layer on the receiving element. As stated above, the hardening agent is preferably used in a 50% aqueous solution by weight although said hardening agent may also be used without dilution. The quantity of hardening agent to be used is based on the amount of OH, NH or SH groups in the polymer.

Alternatively, the polymeric receiving layer may first be cast into a film and then hardened by treating said film with a solution of the hardening agent, i.e., by spreading, spraying or flowing said solution over said film or by immersing said film in a solution of the hardening agent.

The degree of hardening desired is also a factor in determining the amount of hardener to be used. It can be readily seen, therefore, that the amount of hardening agent used is not critical and may be varied at the option of the operator depending upon the particular characteristics desired in the image-receiving layer. In a preferred embodiment, when the receiving sheet comprises a mixture of polyvinyl alcohol and poly-4-vinylpyridine in a 2:1 ratio by weight, about 5% of the 50% aqueous solution of hardening agent based on the weight of polyvinyl alcohol is used. The hardening agents may be used in treating polymeric receiving layers either in diluted form or full strength. As stated above, for ease of handling, the hardening agents are generally used in a. 50% aqueous solution.

The following nonlimiting examples illustrate the use of the hardening agents of this invention:

EXAMPLE 2 To an aqueous solution comprising 100 gm. of polyvinyl alcohol and 50 gm. of poly-4-vinylpyridine, on a dry weight basis, was added 10 gm. of the aforesaid Aldocryl Resin X-12. The solution was then cast on a subcoated film support to form a receiving layer.

EXAMPLE 3 To an aqueous solution comprising 100 gm. of polyvinyl alcohol and 50 gm. of poly-4-vinylpyridine, on a dry weight basis, was added gm. of a 50% aqueous solution, by weight, of the acrolein condensate prepared by the reaction, on a 2 to 1 molar ratio, of acrolein and 1,l,3,3-tetramethoxypropane. The solution was then cast on a subcoated film support to form a receiving layer.

The novel hardening agents of this invention have ben found to provide particularly good results when the alkaline aqueous processing composition is thickened with a cellulosic material, for example, carboxymethyl cellulose or hydroxyethyl cellulose.

Analogous results will also be provided by the remaining condensation products within the preceding generic class designation, expressly including the condensation products of acrolein and the aldehydes and propanes detailed above.

By utilizing the novel hardening agents of this invention, it is possible to avoid the inherent water sensitivity of receiving element polymers and, at the same time, avoid the drawbacks such as adhesion of the positive to the negative, and loss of stability of the negative when stored in the presence of the image-receiving layer, which are noted in many prior art hardening agents, e.g., glutaraldehyde.

The image-receiving layers to be employed in the diffusion transfer process are required to possess certain critical features if photographic images of excellent quality are to be formed therein. During the diffusion transfer processing of an exposed photosensitive sheet, the imagereceiving layer, upon contact with an alkaline processing composition used in diffusion transfer processes, is desired to slightly swell to allow the admittance within the imagereceiving layer of the diffusing image-forming material. This slight swelling should be to such a degree that most if not all of the diffusing image-forming material from the exposed photosensitive sheet may enter and be locked within the image-receiving layer so that a print having the highest image density is formed. However, the swelling should not be to such an extent that the gloss of the final print is destroyed or that the processing composition is induced to adhere to the final print. Extensive swelling of the image-receiving layer can also cause distortion of the formed image. It is within this area that the present invention provides its unusual results in that the process of the present invention provides hardened polymeric receiving layers which are hardened within the desired degree of swellability necessary to provide quality images without loss of gloss or dimensional stability and, most important, while providing an image-receiving layer to which processing composition does not tend to adhere.

The superior qualities of the hardening agents of this invention are demonstrated by a simple test which utilizes the above-described stripping characteristics. The development of an exposed silver halide emulsion is carried out by superimposing said silver halide emulsion on the image-receiving element and spreading therebetween an alkaline aqueous processing composition by inserting the thus-formed sandwich between a set of pressure-applying rollers having a predetermined gap. Hardening agents are not considered acceptable unless the imagereceiving sheet can be stripped without adhesion of the processing composition to said image-receiving layer. Therefore, in order to determine the effectiveness of hardening agents, image-receiving layers which have been treated with hardening agents are processed at roller gaps greatly in excess of what is considered standard and then evaluated for stripping qualities. The thicker the gap, the more likely it is that portions of the processing solution will adhere to the image-receiving layer. For example, it was found that a polyvinyl-alcohol-containing image-receiving layer hardened with glyceraldehyde or malonaldehyde, processed with a roller gap 1 /2 times as thick as a standard gap (0.0040 in.), showed a substantial amount of processing composition adhesion thereto, while similar polymeric layers hardened with the hardening agents of this invention, for example, the acrolein condensate prepared from the reaction between acrolein and 1,1,3,3-tetramethoxypropane or the Aldocryl Resin X-12, stripped cleanly and showed no adhesion of processing composition. The above-described test provides a rapid and reliable measure of the stripping qualities of polymeric receiving sheets treated -with hardening agents. It should be noted that the image-receiving layers treated with the hardening agents of this invention were found to be unusually satisfactory when subjected to this test.

Image-receiving elements, prepared in accordanc with this invention, and particularly those prepared in Examples 2 and 3 above, gave excellent results when employed with multilayer negatives containing dye developers similar to those described in the aforementioned US. Pat. No. 2,983,606.

Th image-receiving elements prepared by the novel process of this invention are especially useful in composite film units intended for use in a Polaroid Land Camera made by Polaroid Corporation, Cambridge, Mass, or a similar camera structure such, for example, as the camera forming the subject matter of US. Pat. No. 2,435,717, issued to Edwin H. Land on Feb. 10, 1948. In general, such composite film units comprise a photosensitive element, an image-receiving element and a rupturable pod containing an alkaline aqueous processing solution. The elements and pod are so associated with each other that, upon processing, the photosensitive element may be superposed on the image-receiving element and the pod may be ruptured to spread the alkaline aqueous processing solution between the superposed elements. The nature and construction of the pods used in such rolls are well known to the art. See, for example, US. Pats. Nos. 2,543,181 and 2,634,886, issued to Edwin H. Land.

Since certain changes may be made in the above products and processes without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. ln a process of forming a photographic image in color, wherein an exposed silver halide emulsion is developed to provide an imagewise distribution of colorproviding materials and said imagewise distribution of color-providing materials is transferred by an aqueous alkaline processing solution to a superposed image-receiving layer to impart to said image-receiving layer a color image, the step of transferring said imagewise distribution of color-providing materials to an image-receiving layer comprising a polymer containing radicals selected from the group consisting of -OH, -NH and -SH radicals, and a hardening agent comprising a condensate of acrolein with a compound selected from the group consisting of: (a) a lower alkylmonoaldehyde, and (b) a tetraloweralkoxypropane.

2. A process as defined in claim 1 wherein said polymer is polyvinyl alcohol.

3. A process as defined in claim 1 wherein said compound is 1,1,3,3-tetramethoxypropane.

4. A process as defined in claim 1 wherein said compound is glyceraldehyde.

5. A process as described in claim 1 wherein said imagereceiving layer comprises about a 2 to 1 mixture of polyvinyl alcohol and poly-4-vinylpyridine and said harden ing agent is a condensate of acrolein and 1,l,3,3-tetramethoxypropane.

6. A process as described in claim 1 wherein said image-receiving layer comprises about a 2 to 1 mixture of polyvinyl alcohol and poly-4-vinyl pyridine and said hardening agent is a condensate of acrolein and formaldehyde.

7. A process as defined in claim 1 wherein said compound is formaldehyde.

References Cited UNITED STATES PATENTS 8 9/ 1964 Haas 9629 5/1965 Fischer et a1. 8127.6

NORMAN G. TORCHIN, Primary Examiner J. R. HIGHTOWER, Assistant Examiner U.S. C1. X.R. 

